#!/usr/bin/node 

const Readable = require('stream').Readable;

let c = 'a'.charCodeAt(0);

class MyReadable extends Readable{

  constructor(){
    super();
  }
  _read(){
    ns.push(String.fromCharCode(c++));
    if(c>'z'.charCodeAt(0)) ns.push(null);
  }
}

let ns = new MyReadable;

ns.pipe(process.stdout);
